The invention relates to spunbonded nonwoven fabrics possessing light stability, particularly ultraviolet, suitable for substrates used to manufacture outdoor covers. In particular, the invention relates to nonwoven fabrics made using a combination of at least two hindered amine light stabilizers, hydroxyl amine and phosphite processing aids; and a carrier resin of polypropylene, polyethylene or a mixture of both. The resulting spunbonded fabric layer has enhanced trapezoidal tear in both the MD and CD directions.
Nonwoven fabrics possessing light stability (particularly ultraviolet) are desirable for use as substrates to manufacture outdoor covers. Outdoor covers include marine, automobile, bike and recreational vehicle covers. Such covers include protecting the vehicle from wear and tear caused by wind, rain and sunlight. Nonwovens and nonwoven composites for such covers are available in the market. However, it was not possible hitherto to incorporate UV stability and still obtain high fabric strength, particularly trapezoidal tear strengths needed for downstream ultrasonic converting. To overcome these problems the invention provides a nowoven product and process for producing such a fabric, having enhanced trapezoidal tear, suitable for further ultrasonic lamination.
In general hindered amine light stabilizers (HALS) are known in the art. For example, published European patent application EP 0792911 A2 to Tennesen discloses a phosphate based flame retardant combined with alkoxyamine functional hindered amine light stabilizer (NOR-HALS) used to achieve flame retardant properties that are better than those with phosphates alone.
U.S. Pat. No. 5,393,812 to Haley describes fibers and fabrics, as used clothing, upholstery and carpeting which contain about 0.01 to 3% (preferably 0.2 to 1.0%) by weight of the composition, of a light stabilizer. This patent discloses a polyolefin, a NOR HALS (alkoxy amine functional hindered amine light stabilizers) and a phosphorous flame retardant (col. 2 line 33-40; col. 4 line 62-64). Regular HALS (hindered amine light stabilizers) may be employed additionally or in place of NOR HALS.
U.S. Pat. No. 5,096,950 to Galbo discloses numerous N-OR1 alkoxy hindered amine light stabilizers.
U.S. Pat. No. 5,200,443 to Hudson discloses a nonwoven web of polypropylene polymer containing an acetylated hindered amine light stabilizer and a hindered amine substituted siloxane.
U.S. Pat. No. 5,004,770 to Cortolano; U.S. Pat. No. 5,124,378 to Behrens; U.S. Pat. No. 5,939,341 to Brown and U.S. Pat. No. 5,300,647 to Malherber all disclose formulations of particular hindered amine light stabilizers.
None of the known prior art discloses a spunbonded nonwoven fabric with UV stability having enhanced durablity. Further, the known art has not disclosed the synergistic effect of combining at least two hindered amine light stabilizers to produce a spunbonded nonwoven fabric having enhanced trapezoidal tear properties.
Thus it is a broad object of the invention to provide a spunbonded nonwoven fabric with UV light stability. Specifically, the fabric layer is made of a base (or virgin) resin polypropylene which is combined with melt processing additives. These additives are a mixture of (i) at least two hindered amine light stabilizers (HALS); (ii) processing aids which are either hydroxyl amines or phosphites or a combination of both; and (iii) a carrier resin of either polypropylene or polyethylene or a mixture of both. Pigments are also included in the formulations to impart desired color properties to the resulting fabrics. The additives are incorporated into a base polyolefinic resin to form a homogeneous blend which is then spunbonded to form the fabric layer.
Another object of the invention is to provide a spunbonded fabric structure possessing at least two layers of spunbond (SB) webs to which suitable melt processable additives have been incorporated to the virgin resin before melt spinning.
A specific object of the invention is to provide spunbond cover substrates having spunbond-spunbond (SS), spunbond-spunbond-spunbond (SSS) and spunbond-spunbond-spunbond-spunbond (SS-SS) composite structures all having enhanced trapezoidal tear strength.
Another more specific object of the invention is to provide spunbond structures having a useful service life from six to sixty months, depending on the desired end use.
Another specific object of the invention is to provide a spunbond fabric that possesses superior initial physical properties as measured by grab/strip tensile tests and trapezoidal tear tests.
A further object of the invention is to provide a spunbond fabric that does not suffer a loss of more than 50% of its initial MD, CD tensiles and initial MD, CD trapezoidal tear values at the end of its useful service life.
A further specific object of the invention is to provide a spunbond fabric wherein the color shift is maintained within tolerances over the entire service life.
The present invention provides a spunbond fabric possessing UV light stability for use as a substrate to manufacture outdoor covers.
The spunbonded fabric comprises a base resin selected from the group consisting of polypropylene and polyethylene combined with melt processable additives. The melt processable additives are a mixture of (i) at least two hindered amine light stabilizers; (ii) a processing aid selected from the group consisting of hydroxyl amines and phosphites; and (iii) a carrier resin selected from the group consisting of polypropylene and polyethylene. Pigments are also included in the formulations to impart desired color properties to the resulting fabrics.
The base resin and melt processable additives are combined to form a homogeneous blend which is then spunbonded to form a nonwoven fabric layer.
The nonwoven fabric of the invention may comprise multiple fabric layers. Fabric structures encompassed by the invention include spunbond (SB), spunbond-spunbond (SS), spunbond-spunbond-spunbond (SSS), spunbond-spunbond-spunbond-spunbond (SS-SS) nonwoven fabrics.
Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention are considered with reference to the drawings, which should be construed in an illustrative and not limiting sense as follows: